These lakes form in an interesting way. Permafrost is permanently frozen soil lying beneath a layer 0.6 to 4 meters thick of soil that thaws in the summer and refreezes in the winter: the active layer. The permafrost itself can be much thicker—up to 1500 meters in parts of Siberia!

As far as I can tell, talik is permanently unfrozen soil on top of, amid or beneath the permafrost.

Permafrost is rock-hard and solid. Liquid water does not pass through it, so permafrost environments tend to be poorly drained and boggy. But when permafrost starts to melt, it becomes soft. Soil sinks down into marshy hollows separated by small hills, forming a kind of terrain called thermokarst.

Trees in this terrain can lean crazily as their roots sink, creating drunken forests.

On flat ground, melted water can pool into a thermokarst lake. On slopes, water pours downhill and the land can rip open in a thermokarst failure. Here are Breck Bowden and Michael Gooseff exploring a thermokarst failure in Alaska:

All these are natural processes that are widespread at the end of each glacial period. Here’s a surprisingly delightful book which discusses this in detail:

• Evelyn C. Pielou, After the Ice Age: the Return of Life to Glaciated North America, U. Chicago Press, Chicago, 1991.

So, please don’t misunderstand: I’m not trying to say that thermokarst lakes, drunken forests and the like are signs of disaster. However, as the Earth warms, new regions of permafrost are melting, and we’ll see these phenomena in new regions. We need to understand how they work, and the positive and negative feedbacks. For example, thermokarst lakes are darker than their surroundings, so they absorb more sunlight and warm the area.

One day in 2007, on the plain in northern Alaska, a lightning strike set the tundra on fire.

Historically, tundra, a landscape of lichens, mosses and delicate plants, was too damp to burn. But the climate in the area is warming and drying, and fires in both the tundra and forest regions of Alaska are increasing.

Scientists have calculated that the fire and its aftermath sent a huge pulse of carbon into the air — as much as would be emitted in two years by a city the size of Miami. Scientists say the fire thawed the upper layer of permafrost and set off what they fear will be permanent shifts in the landscape.

Up to now, the Arctic has been absorbing carbon, on balance, and was once expected to keep doing so throughout this century. But recent analyses suggest that the permafrost thaw could turn the Arctic into a net source of carbon, possibly within a decade or two, and those studies did not account for fire.

“I maintain that the fastest way you’re going to lose permafrost and release permafrost carbon to the atmosphere is increasing fire frequency,” said Michelle C. Mack, a University of Florida scientist who is studying the Anaktuvuk fire. “It’s a rapid and catastrophic way you could completely change everything.”

By the way, if you click on these scientists’ portraits, you’ll see where they work. If you’re a student looking for an interesting career, consider these options! For example, Michelle C. Mack—shown above—runs a lab, and you can see her postdocs and grad students, and what they do.

John Baez wrote, “However, now the Earth is starting to warm beyond what was seen in previous interglacial periods.”

I’m not trying to be argumentative, stupid or difficult but I tend to question throw-away statements that are assumed and can have a big effect on a discussion. In this case, I jumped to Wikipedia where I found the following,

The Antarctic temperature records indicate that the present interglacial is relatively cool compared to previous interglacials, at least at these sites. The Liesecki & Raymo (2005) sediment reconstruction does not indicate significant differences between modern ice volume and previous interglacials, though some other studies do report slightly lower ice volumes / higher sea levels during the 120 ka and 400 ka interglacials (Karner et al. 2001, Hearty and Kaufman 2000).

Qualified with the statement,

However, since geological records such as ice cores and sediments represent an average often on the scale of thousands of years, direct comparison to current values can be misleading. Larger, short term variations in ancient climate are not present in the fossil record. Hence the comparison is not comparing like with like and is scientifically invalid.

My conclusion from five minutes of specific research (and years of experience) is that we don’t really know how the earth’s current “temperature” compares with that of previous interglacial periods. Contradictory evidence is welcome.

Okay, I’ve corrected my post. I thought it would take about 3°C of warming to push us up above the temperatures we’ve seen recorded in ice cores. From the graph you linked to that seems roughly right if we believe the Vostok ice core… but the EPICA ice core makes it look more like 6°C. Of course the International Energy Agency says in its 2011 World Energy Outlook that:

In the New Policies Scenario, cumulative CO2 emissions over the next 25 years amount to three-quarters of the total from the past 110 years, leading to a long-term average temperature rise of 3.5°C. China’s per-capita emissions match the OECD average in 2035. Were the new policies not implemented, we are on an even more dangerous track, to an increase of 6°C.

Being a pessimist, I consider a 6°C rise perfectly plausible over the next century or two. But anyway, my sentence was misleading, and this whole issue of whether we surpass previous interglacials is not quite relevant to my main point, namely that we should learn more about melting permafrost and its effects… so I’ve rewritten it. Thanks!

What is going on with the Arctic climate is not straightforward to understand. Recent attribution studies … have argued that the warming in recent decades, along with the sea ice decrease, is approximately half natural, half anthropogenic … The challenge is to sort out the following:

Russian scientists have recently found more new craters in Siberia, apparently formed by explosions of methane. Three were found last summer. They looked for more using satellite photos… and found more!

How To Write Math Here:

You need the word 'latex' right after the first dollar sign, and it needs a space after it. Double dollar signs don't work, and other limitations apply, some described here. You can't preview comments here, but I'm happy to fix errors.